Trusses in ANSYS

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Transcript Trusses in ANSYS

EMA 405
Tips for Using Truss Elements in ANSYS
Truss Elements in ANSYS
We don’t really need to “mesh” a truss
 Just define nodes directly
(Modeling/Create/Nodes/In Active CS)
 All you need is one element per “line” in the
truss model
 Then create elements
Numbered/Thru Nodes)
 Apply boundary conditions and loads to
Truss Element Types in ANSYS
Besides trusses, link elements are commonly used to model
cable systems, springs (k=EA/L), and actuator arms. ANSYS
has 5 link elements in its library.
Link1 – 2D spar: Model must be completely in x-y plane
Link8 – 3D spar
Link10 – Bilinear 3D Spar: allows for the creation of tension only or
compression only elements. Useful for modeling cables or
contact only supports
Link11 – ANSYS calls this a linear actuator, but it can be thought of as a
shock absorber as damping as well as spring stiffness is applied.
Link180 – 3D finite strain spar: similar to link8 but with improved nonlinear
capabilities. The higher number indicates this is a newer
element in the ANSYS family.
Post Processing
To get stresses in elements, go to: General
Postproc/List Results/Element Solution
and then Stress/Line Element Results
A Test Problem
E=200 GPa
 =0.27
 A=2 cm2
 Use 2-D spar
 Expected results:
smax=2.6 MPa
35 cm
50 cm
F=300 N
Changing Element Properties
If you want to alter the properties of
elements after they are created
◦ Create second set of properties (real
constants, element type, material properties,
◦ Then go to Modeling/Move or
Modify/Elements/Modify Attrib
To check, go to List/Elements
A Slight Modification
Now switch “angled” bar to E=300 GPa
and A=4 cm2
 Expected Results: dmax=13.4 microns;
smax=1.31 MPa
Getting Results From the Element Table
For line elements (links, beams, etc. ) the Element Table is used to access
results data. The Element Table is different for each element, therefore, we need
to look at the help file for LINK1 or LINK8 (Type help link8 in the command
line). From Table 8.2 in the Help file, we can see that the stress (SAXL) can be
obtained 1using the item 'LS,1‘, and the element load (MFORX) using ‘SMISC,1”.
Element Table Continued
From the General Postprocessor menu select Element Table >Define Table
Click on 'Add...'
Type in a label (I used stress)
Scroll down through the items and select by sequence number
Select LS and then type 1 after LS, and hit apply
In a similar manner, add an entry for the element forces (SMISC,1)
These items may now be plotted or listed
Numbering and Load Labels
The numbers associated with the nodes and elements may be displayed using
Plot Controls >Numbering. To show the material or real constant associated
with each element, select that item from the Elem/Attribute scroll list.
The load and boundary condition labels can be refreshed by Plot Controls
>Symbols and selecting all applied B.C.s